Past exam of the mathematics course of the University of Cambridge 2024 iii Paper 218 3 e ii Solution Created 2026-09-24 Updated 2026-09-25
An unpruned maximal CART classifier repeatedly cuts with vertical or horizontal lines until every terminal rectangle is pure or contains observations that cannot be separated by an axis-aligned split. Here the distinct grid points can be isolated into pure rectangles, producing a step-shaped, axis-aligned decision boundary and zero training error.